The present invention relates to a variable volume container whose volume changes as a piston member fitted therein moves.
The variable volume container of this type is employed for example as a container for ink used in stencil printing. In stencil printing machines, ink is supplied to the inner side of a cylindrical printing drum, and the ink is transferred onto a printing sheet through a perforated stencil sheet wound around the outer side of the printing drum. The ink container is normally a cartridge type container detachably mounted to the printing drum, and printing ink is fed from the ink container into the printing drum.
FIG. 10 shows how the ink container 1 is mounted into the printing drum 2. The printing drum 2 is formed to have a cylindrical shape with an ink-permeable circumferential surface which rotates around the central axis of the printing drum. The ink fed into the printing drum 2 from the ink container 1 is pressed toward the outer side of the printing drum 2 by a squeegee roller 3 which rotates as it is in contact with the inner circumferential surface of the printing drum 2. A doctor roller 4 is provided obliquely over and parallel to the squeegee roller 3 with a small gap therebetween, and thereby an ink hold portion P is formed at the valley portion formed between the squeegee roller 3 and the doctor roller 4.
An ink pump 5 is provided in the printing drum 2 to supply printing ink from the ink container 1. The ink pump 5 includes a suction conduit 5a detachably coupled to the outlet 1a of the ink container 1, and an outlet conduit 5b in communication with an ink distribution tube 6 supported parallel to and above the ink hold portion P. Ink sucked and supplied from the ink container 1 using the ink pump 5 is supplied to the ink hold portion P through the outlet conduit 5b and the ink distribution tube 6.
The ink container 1 is formed into a cylinder/piston type container, and the outlet 1a is formed at an end wall 1c that blocks a front end of the cylinder 1b (the right end in FIG. 10). The back end of the cylinder 1b (the left end in FIG. 10) is sealed by a piston member 1d slidably fitted into the cylinder 1b, and thus an ink storage chamber 1e is formed between the end wall 1c and the piston member 1d. The amount of ink contained in the ink storage chamber 1e is reduced as the ink is sucked using the ink pump 5, and as a result the piston member 1d moves toward the front end of the cylinder 1b in the sealed state. The ink container 1 having such a structure is distributed in the market as it has its outlet 1a sealed with a cap 1f as shown in FIG. 11, and when the ink container 1 is used, the outlet 1a removed of the cap 1f is inserted into the suction conduit 5a of the ink pump 5. As shown by the double dotted chain line in FIG. 11, the back end of the cylinder 1b (the upper end in FIG. 11) is provided with a simple cover 7 having an opening, in order to prevent the piston member 1d from coming out.
However, if the ink container 1 is transported or stored in a distribution channel with the cap 1f facing upward, ink could leak from a gap between the piston member 1d and the inner wall of the cylinder 1b, or the piston member 1d could go down by the weight of ink, causing air to enter the ink storage chamber 1e from a gap between the outlet 1a and the cap 1f and mix into the ink. Therefore, the cap side of the container 1 is preferably faced downward as shown in FIG. 11, in other words, the ink container 1 is preferably placed upside down in packing into a box or in display.
As can be seen from FIG. 11, however, the outlet 1a of the ink container 1 is formed to have a diameter smaller than the diameter of the cylinder 1b. As a result, the following disadvantages are encountered if the container 1 is placed with the smaller-sized outlet 1a being faced downward.
(1) This smaller-sized outlet 1a or the cap 1f has to support the entire load of the ink container 1 and the content thereof, and therefore the ink container 1 becomes unstable, and can be easily turned over even by slight vibration.
(2) At the time of packaging, transporting and unloading, if the container 1 is impacted or dropped, impact force could be concentrated at the outlet 1a, causing damage to the outlet 1a and thereby causing leakage of ink from the cylinder 1b. 
In recent years, in order to increase the storage amount of ink, there is a demand that diameter of the cylinder 1b is enlarged as far as the cylinder 1b is accommodated in an attachment space of the printing drum 2. In this case, the outlet 1a would be even smaller as compared to the enlarged cylinder 1b, which makes the disadvantages even more serious.
It is an object of the present invention to provide a variable volume container which has an improved structure in the vicinity of the outlet and is capable of stably holding the outlet facing downward even if the cylinder of the container is enlarged in diameter.
According to the present invention, the above-described object is achieved by a variable volume container comprising a cylindrical main body having an end wall at an end thereof; an outlet projecting from an outer surface of said end wall for allowing a content to be supplied; a piston member fitted into said main body sealingly and slidably in an axial direction of said main body for defining a variable volume storage chamber between itself and said end wall; a plug member detachably mounted to said outlet; and an impact resisting reinforcement disposed at said end wall.
In this structure, the storage chamber is sealed by the plug member that is attached to the outlet projecting from the end wall. If the container is placed upside down with the outlet facing downward in the sealed state, the entire load of the container including the weight of the content acts upon the outlet. If impact in a vertical direction is applied to the container in this state, impact force concentrates at the outlet, particularly at the root portion of the outlet. However, since the impact resisting reinforcement is provided at the end wall from which the outlet projects, the root portion of the outlet is protected by the impact resisting reinforcement and is prevented from being damaged.
The impact resisting reinforcement may be a part of said end wall having a thickness gradually increased toward said outlet. This thickness increasing part is thickest and strongest at the outlet, and therefore improves the strength of the root portion of the outlet to effectively protect the root portion against impact and prevent the outlet from being damaged.
In addition, the impact resisting reinforcement may be formed as a rib shaped projection disposed on an outside surface, an inside surface, or both outside and inside surfaces of said end wall. The rib shaped projection reinforces the end wall provided with the outlet, and protects the root portion of the outlet, so that the outlet will not be damaged.
The rib shaped projection is preferably disposed in contact with an outer periphery of a projecting part of the outlet. In this case, the outer periphery of the projecting part of the outlet is supported by the rib shaped projection, and thus the outlet will not be deformed by bending or buckling, or damaged even when impact is applied thereto.
The rib shaped projection preferably extends beyond a line connecting a periphery of a head of said plug member mounted to said outlet and a periphery of said end wall. When the height of the rib shaped projection is at least beyond the line connecting the periphery of the head of the plug member and the periphery of the end wall, the impact applied to the outlet can be avoided or alleviated.
Furthermore, it is preferred that the rib shaped projection is gradually broadened toward the end wall, so that a corner portion formed between the rib shaped projection and the end wall is rounded. The corner portion having such a circular arc surface can prevent stress from concentrating at the root portion of the rib shaped projection. Therefore, the effect of the rib shaped projection to reinforce the end wall can further be improved.
Furthermore, preferably, the plug member has a head with an expanded diameter in a direction perpendicular to an axis of said cylindrical main body and a larger area than said outlet, and has a leg portion which projects from said head and is in abutment against said end wall. In this case, the main body is supported by the surface of the expanded head of the plug member and thus is placed stably. Also, any impact applied to the head is allowed to escape to the end wall through the leg portion, and thus the impact directly applied upon the outlet can be alleviated so that the outlet is prevented from being damaged.
In addition, in each of the variable volume containers described above, the storage chamber can store a high viscosity material, such as printing ink for use in stencil printing. In this case, the variable volume containers can be used as an ink container received in a stencil printing machine. When the ink containers are placed upside down with the outlet at the lower side in packaging/transport, the outlet can be prevented from being damaged during the transport, so that ink will not leak.